This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-321000, filed Oct. 18, 2001. The entire contents of that application are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a distance-measuring technique for a camera, and particularly to a distance-measuring device performing a distance measurement in plural regions in a picture.
2. Description of the Related Art
Conventional auto-focus techniques for a camera are known. Many of the auto-focus techniques focus on an object at the center of a picture (i.e., a bounded image). Therefore, when an object is not in the center area of a picture, the camera is moved so that the object is brought temporarily to the center of the picture and focused upon. Then, after the focusing position is locked, the camera is moved back so that the original composition of the picture is recovered. However, this technique may be too slow for certain situations and require too much skill for a casual user.
U.S. Pat. No. 4,637,705 discloses a technique in which correct, or at least improved, focusing is accomplished regardless of the position of an object in a scene, even where there is no object at the center of the picture. More specifically, this technique uses multiple distance-measuring points in the picture (multi AF).
In many photographs, however, a principal object exists at the center of a picture. Therefore, as more points in an image are measured for purposes of auto-focus, the probability of taking a picture with the wrong focus position increases. Concerning this point, the prior patent ignores results that deviate from a predetermined distance range.
However, in the prior patent, the focus position is judged solely by distance-measuring results. Therefore it is difficult to determine whether the focus should be adjusted on the center of the picture, or on an area at the periphery of the picture. If the center of the picture is focused on, and the principal object (e.g., a person) is in an area at the periphery of the picture, the principal object will not be in focus. On the other hand, if the periphery of a picture is focused on and the principal object (e.g., a person) is in the center of the picture, the principal object will not be in focus.
In view of the foregoing limitations of the prior autofocusing technique, a distance-measuring device for a camera having a high possibility of enabling a correct focusing, regardless of an object""s position in a picture, is needed.
In the present invention, a distance-measuring device of a camera judges, in the selection of a principal object, whether an object is fully included in a picture. If it is not fully included, it is determined not to be the principal object. If an object is judged not to be the principal object, the object is excluded from focusing targets or a focusing precedence of the object is reduced.
In more detail, the distance-measuring device of a camera usually contains the following: a distance-measuring part that detects the distance to an object or objects at multiple distance-measuring points in a picture; and an operation part that excludes a distance-measuring point as a focusing target or lowers a focusing precedence of the object when the distance-measuring point is a member of a group composed of distance-measuring points adjacent to each other within a predetermined distance range, and one of members of the group is adjacent to the boundary of the picture.
The above group preferably contains a distance-measuring point with the shortest object distance.
The above group preferably contains multiple distance-measuring points joined in a direction from a distance-measuring point at the periphery of picture to a boundary of picture.
The above group preferably does not contain a distance-measuring point in the central part of picture.
The determination of the above group preferably includes the following process: (1) selecting a distance-measuring point with the shortest object distance. (2) selecting adjacent distance-measuring points in a direction from the selected distance-measuring point to the boundary of the picture when the above selected distance-measuring point is at the periphery of the picture.
The above distance-measuring part preferably has a common distance-measuring region, and an expanded distance-measuring region on a side or sides of the boundary of the picture with respect to the above common distance-measuring region. The above group is formed when the distance-measuring point with the shortest object distance in the common distance-measuring region is located at the periphery of the common distance-measuring region. The above group contains the distance-measuring point with the shortest distance in the common distance-measuring region and multiple distance-measuring points in the expanded distance-measuring region joined to the distance-measuring point with the shortest distance.
For example, in the distance-measuring device of the present invention, the distance to an object or objects may be measured in multiple regions (points) on a picture, and the region with the shortest distance to the object is detected and taken as a principal object candidate. In this case, if the principal object candidate is at the periphery of the picture, the object may likely protrude from (i.e., extend beyond the bounds of) the picture. Accordingly, the distance-measuring device examines whether a region having a similar object distance to the above principal object candidate (a region having continuity) continues from the principal object candidate to the boundary of the picture and, if it continues, judges that the principal object candidate protrudes from the picture (the principal object candidate is not fully included in the picture).
The above distance measurement can be obtained, e.g., by trigonometry. Alternatively, or in addition, distance measurement may be performed by receiving a light given by emitting a stroboscopic light towards an object, and then measuring the quantity of reflected light.